The present invention relates to a two-stage supercharging method and apparatus for the supercharging of an internal combustion engine.
A known two-stage exhaust-driven supercharger assembly, disclosed for example in the Swiss Pat. No. 595 941 and the published German patent application No. 27 52 988, have the disadvantage that the exterior dimensions of the low-pressure and the high-pressure superchargers are practically identical. The low-pressure and the high-pressure superchargers have an identical pressure ratio within the low-pressure and the high-pressure compressors. Since the two supercharger shafts are located within one plane, it becomes impossible to install any necessary auxiliary components, such as a bypass valve, a combustion chamber, an air charge intercooler or the like, next to the low-pressure and the high-pressure superchargers in such a manner that a compact two-stage exhaust-driven supercharger assembly will result.
It is an object of the present invention to provide a supercharging method and apparatus which will make possible the construction of a truly compact two-stage exhaust-driven supercharger aggregate.
The present invention accomplishes this object and others by providing a two-stage, exhaust-driven supercharger aggregate wherein the expansion of the exhaust gas is accomplished first within at least one high-pressure turbine and then within one low-pressure turbine. In addition, the compression of the fresh air to be fed into the internal combustion engine is accomplished first in a low-pressure compressor and then in at least one high-pressure compressor.
In a preferred embodiment, the pressure ratio of the low-pressure compressor is at least 3:1 and preferably at least 4:1, and the pressure ratio of the high-pressure compressor is no more than 3:1 and preferably no more than 2:1. Also, it is preferred that the total pressure ratio of the exhaust-driven supercharger aggregate is at least 6:1 and preferably at least 8:1.
The present invention also provides for cooling the fresh air to be fed into the internal combustion engine after it emerges from the high-pressure compressor. Preferably the fresh air is also cooled after emerging from the low-pressure compressor.
In order to influence the operating characteristic within the compressor performance graph, to improve the behavior under partial load, and to influence operations under full and/or partial load as well as to meet special operating characteristics of the internal combustion engine to be supercharged, it is preferred to feed a portion of the compressed supercharger air emerging from the high-pressure compressor into the intake of the high-pressure turbine by way of a bypass and control device. The portion of the compressed supercharger air is mixed with the exhaust gas from the internal combustion engine. The mixture of exhaust gas and the supercharger air is then heated and fed into the intake of the high-pressure turbine. The heating is preferably accomplished in a combustion chamber arranged prior to the inlet of the high-pressure turbine.
In a preferred embodiment of the apparatus of the present invention, the front end of the low-pressure supercharger is formed by the exterior parts of the low-pressure supercharger which are in the most outward position in an axial direction. In order to conserve space when charging a V-engine it is preferred to provide the exhaust-driven supercharger aggregate with at least two high-pressure superchargers which are connected with the low-pressure supercharger. The axes of the two high-pressure superchargers are arranged in an offset manner relative to the axis of the low-pressure supercharger and at least approximately symmetrically to each other.
In this arrangement, it is preferred to arrange the turbine and/or the compressor of the high-pressure and/or the low-pressure supercharger in multi-stage form.
In addition, the exhaust gas to be fed into the intake of the high-pressure turbine may be heated in a combustion chamber arrangement prior to the admixture with a portion of the compressed supercharger air emerging from the high-pressure compressor.